Side by side
IFMGA mountain guide: rock and ice climbing, glacier travel, alpine summits, ski mountaineering. The only qualification for terrain requiring a rope.
IML (UIMLA international mountain leader): summer and winter hiking on non-glaciated terrain worldwide, including hut-to-hut treks, snowshoeing and remote multi-day walking.
National awards: many countries also run their own hiking-guide and single-pitch awards that are valid in that country only. They can be entirely appropriate for local trails.
Choosing for your trip
If the route crosses a glacier, needs a rope, or is graded as climbing or via ferrata, book IFMGA. If it is a walking route on marked or wild trails without those elements, an IML is qualified, more widely available and usually cheaper.
Related questions
Can an IML guide a via ferrata?
Generally no. Via ferrata and any roped protection sit outside the IML scope in most countries, though some national awards add a specific via ferrata module.